Golf ball

ABSTRACT

The object of the present invention is to provide a golf ball having excellent luster and durability. The golf ball of the present invention comprises a golf ball body and a paint film covering the golf ball body, wherein the golf ball body and the paint film contains a luster material having a particle size of 5 μm to 100 μm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improving an appearance of a golf ball, more particularly to improving an appearance (luster and durability of a paint film) of a golf ball.

2. Description of the Related Art

A golf ball is normally colored white, but there has been an increasing demand for a golf ball with an enhanced quality and an individualized appearance. In response to such a demand, a golf ball provided with luster has been proposed.

For example, Japanese patent publication No. 2004-166719 proposes a golf ball provided with a mark formed on a surface of the golf ball body and a transparent covering layer covering the mark, wherein the transparent covering layer comprises a base resin and a luster material of a glass flake having a surface thereof covered with a metal oxide, and covers the mark that has a color tone satisfying L≦40 when represented by Lab system. Since the transparent covering layer covering the mark includes the luster material, it is possible to provide the golf ball with luster without lowering durability of the mark and the paint film itself.

Japanese patent publication No. 2005-52510 discloses a golf ball comprising a core and a cover having two or more layers covering the core, wherein a base material of an outermost layer cover of the cover is a thermoplastic resin in which 0.2 to 5 parts by mass of a cholesteric liquid crystal polymer is included based on 100 parts by mass of the thermoplastic resin, and wherein a base material of an inner cover adjacent to the outermost layer cover is a thermoplastic resin in which 1 part by mass or less of titanium oxide and 1 part by mass or less of a fluorescent pigment are included respectively based on 100 parts by mass of the thermoplastic resin.

Japanese patent publication No. H06-170013 discloses a golf ball containing a pigment developing color by an interferential action of reflected lights in a paint layer on a ball surface or a ball body, the hue of which changes depending on an angle from which it is viewed.

Japanese patent publication No. H11-151322 discloses a golf ball having a pearl color comprising a core and a cover covering the core, wherein the cover contains 0.02 to 1.5 parts by weight of a mica pigment, 1.0 to 5.0 parts by weight of titanium oxide and less than 5 parts by weight of a fluorescent pigment based on 100 parts by weight of the resin.

SUMMARY OF THE INVENTION

If the luster material is blended only in the cover of the golf ball, the luster material may not be able to exhibit its luster sufficiently due to opacity of the cover material.

If a content of the luster material is increased in order to allow the luster material to exhibit luster, there arises a problem of the weld lines becoming conspicuous when the cover is formed. Additionally, the durability of the golf ball may also be lowered. On the other hand, when the luster material is blended only in the paint film of the golf ball, there may be a case where a luster material clogs a paint line of the paint to generate unevenness of paint application, resulting in unevenness of appearance.

The present invention has been achieved in view of the above circumstances. The object of the present invention is to provide a golf ball having uniform and excellent luster and excellent durability.

The present invention provides a golf ball having a golf ball body and a paint film covering the golf ball body, wherein each of the golf ball body and the paint film contains a luster material having a particle size of 5 μm to 100 μm.

According to the present invention, since the luster material is blended in both the paint film and the cover, a golf ball having a good appearance with luster can be obtained. A particle size of the luster material is 5 μm to 100 μm, and when molding the cover, there is no problem of weld line being conspicuous, and when applying a paint, there occurs no clogging of a paint line so that unevenness of paint application hardly occurs.

The luster material preferably, for example, comprises mica as a core layer and a light-reflective material covering a surrounding area of the core layer. More preferably, the luster material comprises mica as the core layer and the light-reflective material consisting of a titanium oxide or an iron oxide covering a surrounding area of the core layer. Additionally, it is also a preferred embodiment that the golf ball body has a cover and the cover contains 0.1 part to 5 parts by mass of the luster material based on 100 parts by mass of the resin component constituting the cover. Further, it is preferred that the paint film contains 1 part or more and 20 parts or less of the luster material based on 100 parts of the resin component included in the paint film by mass.

The present invention can provide a golf ball having excellent luster and durability. The golf ball also has good coating workability, and the paint film to be formed has no unevenness of paint application and has good durability. According to the present invention, there is no problem of weld line becoming conspicuous when molding the cover.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A golf ball of the present invention comprises a golf ball body and a paint film covering the golf ball body, wherein each of the golf ball body and the paint film contains a luster material having a particle size of 5 μm to 100 μm.

First, the luster material used in the present invention will be explained. The present invention contains a luster material having a particle size of 5 μm to 100 μm (hereinafter simply referred to as “luster material” occasionally).

In the present invention, having a particle size of 5 μm to 100 μm means that the particles of 80% or more of the total volumes of the particles have a particle size in a range of 5 μm to 100 μm. In the present invention, preferably used is a luster material having a particle size of 5 μm to 80 μm, more preferably a luster material having a particle size of 5 μm to 60 μm.

If the particle size is outside the above range, when forming a cover, a weld line becomes conspicuous so that the appearance of the resultant golf ball will be undermined. In forming the paint film, clogging of a paint line including a spray gun and the like becomes more likely to occur, causing unevenness of paint application.

The particle size can be measured by, for example, a laser diffraction method using a mastersizer manufactured by Marvern.

Examples of the luster material used in the present invention include a luster material having a core layer covered with one or more layers of a light-reflective material, such as the luster material having a core layer consisting of mica, a pearl flake, a glass flake, a metal or a metal oxide, and a light-reflective material consisting of a metal, a metal oxide, or a metal nitride and covering the surrounding area of the core layer. Examples of the metal of the core layer include at least one kind selected from the group consisting of aluminum, chromium, cobalt, gold, silver, nickel, and iron. Examples of the metal oxide used for the core layer and the light-reflective material include titanium dioxide, iron oxide and the like.

Specific examples of the luster material include, for example, a luster material having a core layer consisting of mica and a metal oxide consisting of titanium oxide or iron oxide covering a surrounding area of the core layer (“Iriodin” manufactured by Merck Ltd.), a luster material having a core layer consisting of a glass flake and a metal oxide consisting of titanium dioxide or iron oxide or a metal such as gold, silver, and nickel covering a surrounding area of the core layer (“Metashine” manufactured by Nippon Sheet Glass Co., Ltd.), and a luster material having a core layer consisting of aluminum or an iron oxide and a metal oxide consisting of silicon dioxide or iron oxide covering a surrounding area of the core layer (“Variocrom” manufactured by BASF).

In the present invention, a photochromic laminated body formed by laminating polymer layers having different refractive index, preferably a photochromic laminated body formed by laminating two kinds of polymer layers having different refractive indexes alternately may be used as the luster material. The photochromic laminated body is considered to exhibit the excellent luster due to the following mechanism. Namely, incident lights entering into the photochromic laminated body from the outside reflects at the surface of the laminated body and at the interface of the multi layer structure, and these reflected lights interfere with each other. Then, since polymers having different refractive indexes are laminated, a reflected light having a specific color is strengthened depending on a film thickness of the polymer layer and the number of laminated layers and the like, and thus the metallic luster having a subtly different colors are developed depending on an angle from which they are viewed. Specific examples of the photochromic laminated body include, for example, “Morphotone” manufactured by TEIJIN FIBERS LIMITED.

The golf ball of the present invention is a golf ball comprising a golf ball body and a paint film covering the golf ball body, wherein each of the golf ball body and the paint film comprises the luster material having a particle size of 5 to 100 μm. Namely, a golf ball having the excellent luster can be obtained by including the luster material in both of the golf ball body and the paint film covering the golf ball body.

Hereinafter, a paint film containing the luster material will be explained.

The paint film may be provided in a manner that it covers the golf ball body. The paint film may be what is called a clear paint layer containing a resin component and the luster material without another pigment, or may be what is called an enamel paint layer containing a resin component, the luster material and another pigment. It is preferably the clear paint layer.

The resin component constituting the paint film is not particularly limited, and an acrylic resin, an epoxy resin, a polyurethane resin, a polyester-based resin, a cellulose-based resin and the like may be used, but a two-component curing type polyurethane resin to be mentioned later is preferably used. If the two-component curing type polyurethane resin is used, a paint film which is further excellent in durability can be obtained.

The two-component curing type polyurethane resin is a polyurethane resin obtained by reacting a base resin and a curing agent. Such examples include one obtained by curing a base resin containing a polyol component with a polyisocyanate compound or a derivative thereof.

The base resin containing the polyol component preferably contains a specific urethane polyol as shown in the following. The urethane polyol is synthesized by a reaction between a polyisocyanate and a polyol. The polyisocyanate used for the synthesis is not particularly limited as long as it has two or more isocyanate groups. Such examples include an aromatic polyisocyanate such as 2,4-toluene diisocyanate, 2,6-tolylene diisocyanate, the mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylene diisocyanate (PPDI); and an alicyclic or aliphatic polyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), norbornene diisocyanate (NBDI). These may be used either alone or as a mixture of at least two of them. Among them, in view of weather resistance, a non-yellowing type polyisocyanate such as TMXDI, XDI, HD₁, H₆XDI, IPD₁, H₁₂MDI, and NBDI is preferably used. The polyisocyanate may also be used as a curing agent for curing the urethane polyol.

The polyol used for preparing the urethane polyol is not particularly limited as long as it has a plurality of hydroxyl groups. Such examples include a polyol having a low-molecular weight and a polyol having a high molecular weight. Examples of the polyol having a low-molecular weight include a diol such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; and a triol such as glycerin, trimethylol propane, and hexanetriol. Examples of the polyol having a high molecular weight include a polyether polyol such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), polyoxytetramethylene glycol (PTMG); a condensed polyester polyol such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); a lactone polyester polyol such as poly-ε-caprolactone (PCL); a polycarbonate polyol such as polyhexamethylene carbonate; an acrylic polyol and the like. Among the polyols described above, a polyol having a weight average molecular weight of 50 to 2,000, particularly a polyol having a weight average molecular weight of about 100 to 1,000 is preferably used. These polyols may be used either alone or as a mixture of at least two of them.

The urethane polyol is a polyol wherein a urethane bond is formed by a reaction between the polyisocyanate and a polyol, having a hydroxyl group at a terminal thereof. Herein, a ratio of the urethane bonds in the urethane polyol is preferably 0.1 mmol to 5 mmol in 1 g of the urethane polyol. A ratio of the urethane bonds is related to rigidity of the paint film to be formed, and if it is less than 0.1 mmol/g, urethane concentration of the paint film to be formed becomes low so that abrasion-resistance may become insufficient. On the other hand, if it is more than 5 mmol/g, the paint film becomes too hard, so that flexibility of the film with the deformation of the golf ball body becomes lowered and more susceptible to cracking.

A weight average molecular weight of the urethane polyol is preferably 4,000 or more, more preferably 4,500 or more, and preferably less than 10,000, more preferably 9,000 or less. If it is less than 4,000, it takes a long time to dry, so that workability and productivity becomes lowered. On the other hand, if the urethane polyol has a high molecular weight of 10,000 or more, the hydroxyl value of the urethane polyol becomes relatively small, so that an amount to be reacted after coating becomes small and thus adhesion to a base (golf ball body) tends to be lowered. Additionally, if a weight average molecular weight is 9,000 or less, a dense paint film (or a clear paint layer) which is less in lowering of adhesion even in a state of being wet in water can be formed.

A hydroxyl group value of the urethane polyol is preferably 15 mgKOH/g or more, particularly preferably 25 mgKOH/g or more, and preferably 130 mgKOH/g or less, particularly preferably 120 mgKOH/g or less. If it is less than 15 mgKOH/g, a reaction with the curing agent becomes insufficient, so that adhesion strength with the ball body may become difficult to obtain. On the other hand, if it is more than 130 mgKOH/g, a reaction with the curing agent requires a long time so that a drying time becomes longer to lower the productivity and, at the same time, the ball becomes susceptible to cracking at the time of impact.

The urethane polyol as described above can be obtained by reacting a polyol and a polyisocyanate which are to be raw materials in such a proportion that the hydroxyl groups of the polyol component is in excess relative to the isocyanate groups of the polyisocyanate component by molar ratio. In the above described reaction, a solvent or a catalyst (e.g., dibutyl tin dilaurylate) publicly known for use in a urethane reaction may be used. A ratio of the urethane bond may be adjusted by adjusting a molecular weight of the polyol which is to be a raw material, a blending ratio of the polyol and the polyisocyanate and the like.

The polyol component constituting the base resin is preferably the specific urethane polyol itself; that is, preferably, the base resin is substantially the specific urethane polyol, but, apart from the urethane polyol, may include a polyol which is compatible with the urethane polyol and devoid of the urethane bond, too. In such a case, the polyol devoid of the urethane bond is not particularly limited, and the above-mentioned raw material polyol for syntheizing the urethane polyol may be used. If the base resin contains a polyol devoid of the urethane bond, a content of the urethane polyol in the base resin is preferably 50 mass % or more, more preferably 80 mass % or more. If the content of the urethane polyol in the base resin is less than 50 mass %, the content of the urethane polyol becomes relatively small, so that a drying time becomes longer.

A content of the luster material in the paint film is not particularly limited, but it is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more and 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 13 parts by mass or less based on 100 parts by mass of the resin component. There is a tendency that luster becomes insufficient if the content of the luster material is less than the lower limit, while if it is more than the upper limit, durability of the paint film becomes lowered.

Besides the abovementioned base resin, the paint film may further contain an additive which is included in a paint for a conventional golf ball such as an ultraviolet absorber, an antioxidant, a light stabilizer, a fluorescent brightener, an antiblocking agent, and a pigment.

A mark is normally formed on a surface of the golf ball body. The mark formed on the surface of the golf ball body may be formed by using an ink composition which is normally used for an ink composition for marking a golf ball, for example, one containing a pigment, a solvent, a base resin, other additives and the like. The base resin for the ink composition for marking is not particularly limited, and may include a polyester resin, an epoxy resin, nitrocellulose, an acrylic resin, a vinyl chloride-vinyl acetate copolymer, a polyurethane resin, and a polyamide resin; the epoxy resin, the polyester resin, the nitrocellulose and the like are preferred since they are excellent in adhesion. When the epoxy resin is used as the base resin, for example, it is preferred to use a polyisocyanate such as hexamethylene diisocyanate, isophorone diisocyanate, and tolylene diisocyanate as a curing agent. The solvent of the ink composition for marking is not particularly limited, and may include cyclohexanone, acetylacetone, propyleneglycol monomethylether acetate, methoxymethylbutylacetate, ethylacetate, and aromatic hydrocarbon, or a mixture solvent of at least two of them. The other additives may include a delustering agent, a defoamer and the like, and as a delustering agent, colloidal silica, a low density polyethylene particle, a medium density polyethylene particle and the like may be used. As the defoamer, methyl siloxane and the like may be used.

The golf ball of the present invention has no limitation on its structure and includes a one-piece golf ball, a two-piece golf ball, a three-piece golf ball, a multi-piece golf ball comprising at least four layers, and a wound-core golf ball. The present invention can be applied for all types of the golf ball. Luster of the golf ball can be further enhanced by including the above-mentioned luster material in a one-piece golf ball body in a case of one-piece golf ball, and in an outermost layer cover in a case of a golf ball body having a core and a cover. In a more preferred embodiment of the present invention, the above mentioned luster material is included in an outermost layer cover of the golf ball body having a core and a cover.

Hereinafter, the cover composition forming the cover will be explained. However, components included in the cover composition and the content thereof are same as the components included in the cover and the content thereof unless explained otherwise.

The resin component of the cover composition forming the cover is not particularly limited, and such examples include a polyurethane resin, an ionomer resin, a polyamide resin, a polyester resin, or a mixture of these. Particularly, it is a preferred embodiment that a main component of the resin component is a polyurethane resin or an ionomer resin, and a content of the polyurethane resin or the ionomer resin is preferably 50 mass % or more, more preferably 70 mass % or more, even more preferably 90 mass % or more. Further, it is also a preferred embodiment that the resin component essentially consists of the polyurethane resin or the ionomer resin. If the polyurethane resin or the ionomer resin is employed as the resin component of the cover composition, a cover having excellent durability can be obtained.

The polyurethane resin which can be used for the resin component for the cover composition is not particularly limited as long as it has a plurality of urethane bonds in a molecule. It is, for example, a product in which the urethane bonds are formed in the molecule by reacting a polyisocyanate with a polyol, if necessary, further reacting with a polyamine and the like. Examples of the polyurethane resin include a thermoplastic polyurethane resin, and a thermosetting (two-component curing type) polyurethane resin.

In general, the polyurethane resin preferably contains a polyisocyanate component and a polyol component, and, as necessary, a polyamine component. The polyisocyanate component is not particularly limited as long as it has 2 or more isocyanate groups. Such examples include an aromatic polyisocyanate such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), paraphenylene diisocyanate (PPDI); and an alicyclic or aliphatic polyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), andnorbornene diisocyanate (NBDI). These may be used either alone or as a mixture of at least two of them.

In view of improving the abrasion-resistance, an aromatic polyisocyanate is preferably used as the polyisocyanate component of the polyurethane resin. By using the aromatic polyisocyanate, the mechanical property of the resultant polyurethane resin will be improved, and thus the cover excellent in the abrasion-resistance is obtained. In view of improving the weather resistance, a non-yellowing type polyisocyanate such as TMXDI, XDI, HDI, H₆XDI, IPDI, H₁₂MDI, and NBDI is preferably used as the polyisocyanate component of the polyurethane resin, more preferably 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) is used. 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) has a rigid structure, so that the mechanical property of the polyurethane resin is improved and thus a cover which is excellent in the abrasion-resistance can be obtained.

The polyol component constituting the polyurethane resin is not particularly limited as long as it has a plurality of hydroxyl groups. Such examples include a polyol having a low-molecular weight, a polyol having a high molecular weight and the like. Examples of the polyol having a low-molecular weight include a diol such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; and a triol such as glycerin, trimethylol propane, and hexanetriol. Examples of the high molecular weight polyol include a polyether polyol such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polyoxytetramethylene glycol (PTMG); a condensed polyester polyol such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); a lactone polyester polyol such as poly-ε-caprolactone (PCL); polycarbonate polyol such as polyhexamethylene carbonate; and an acrylic polyol. A mixture of at least two kinds of the polyols described above may also be used.

An average molecular weight of the polyol having high molecular weight is not particularly limited, but it is, for example, preferably 400 or more, more preferably 1000 or more. If the average molecular weight of the high molecular weight polyol becomes too small, the resultant polyurethane becomes hard, resulting in lowering of shot feeling of the golf ball. An upper limit of the average molecular weight of the high molecular weight polyol is not particularly limited, but it is preferably 10000 or less, more preferably 8000 or less.

The polyamine constituting the polyurethane as necessary is not particularly limited as long as it comprises at least two or more amino groups. Examples of the polyamine include an aliphatic polyamine such as ethylenediamine, propylenediamine, butylene diamine, hexamethylenediamine, an alicyclic polyamine such as piperazine and isophoronediamine, and an aromatic polyamine.

The aromatic polyamine has no limitation as long as it has at least two amino groups directly or indirectly bonded to an aromatic ring. Herein, the “indirectly bonded to the aromatic ring”, for example, means that the amino group is bonded to the aromatic ring via a lower alkylene bond. Further, the aromatic polyamine includes, for example, a monocyclic aromatic polyamine having at least two amino groups bonded to one aromatic ring or a polycyclic aromatic polyamine having at least two aminophenyl groups each having at least one amino group bonded to one aromatic ring.

Examples of the monocyclic aromatic polyamine include a type such as phenylenediamine, toluenediamine, diethyltoluenediamine, and dimethylthiotoluenediamine wherein amino groups are directly bonded to an aromatic ring; and a type such as xylylenediamine wherein amino groups are bonded to an aromatic ring via a lower alkylene group. Further, the polycyclic aromatic polyamine may include a poly(aminobenzene) having two aminophenyl groups directly bonded to each other or a compound having at least two aminophenyl groups bonded via a lower alkylene group or an alkylene oxide group. Among them, a diaminodiphenylalkane having two aminophenyl groups bonded to each other via a lower alkylene group is preferable. Typically preferred are 4,4′-diaminodiphenylmethane and the derivatives thereof.

In the present invention, the thermoplastic polyurethane resin is preferably used, and the thermoplastic polyurethane elastomer is more preferably used as the resin component of the cover composition. The thermoplastic polyurethane elastomer used herein is the polyurethane resin having so-called “rubber elasticity.” The use of the thermoplastic polyurethane elastomer provides the cover with high resilience. The thermoplastic polyurethane elastomer is not limited as long as it can be molded into the cover by injection-molding or compression molding. Examples of the thermoplastic polyurethane elastomer are “ELASTOLLAN XNY 90A”, “ELASTOLLAN XNY 97A”, and “ELASTOLLAN XNY585” available from BASF Japan.

In the present invention, it is also a preferred embodiment to use a thermosetting (two-component curing type) polyurethane resin as a resin component of the cover composition. The thermosetting (two-component curing type) polyurethane resin can generate a great amount of three-dimensional crosslinks, so that a cover which is excellent in durability can be obtained. Examples of the thermosetting (two-component curing type) polyurethane resin may include a type in which the isocyanate group terminated urethane prepolymer is cured using a curing agent such as polyamine, polyol and the like, or a type in which a hydroxyl group or an amino group-terminated urethane prepolymer is cured by a curing agent such as a polyisocyanate. The polyamine, the polyol, and the polyisocyanate to be used as the curing agent can be suitably selected from the above described compounds. Among them, as a thermosetting (two-component curing type) polyurethane resin, one obtained by curing the isocyanate group terminated urethane prepolymer with a polyamine is preferred. In such a case, a molar ratio of the amino group of the curing agent with respect to the isocyanate group of the urethane prepolymer (NH₂/NCO) is 0.70 or more, more preferably 0.80 or more, even more preferably 0.85 or more, 1.20 or less, more preferably 1.05 or less, even more preferably 1.00 or less. If it is less than 0.70, an amount of the isocyanate group terminated urethane prepolymer with respect to the polyamine becomes excessive, so that a production reaction of an allophanate cross-linkage and a burette cross-linkage becomes more likely to occur, resulting in insufficient flexibility of the polyurethane to be obtained as a final product. On the other hand, if it is more than 1.20, the isocyanate group becomes insufficient, so that a reaction of the allophanate or a biuret cross-linkage becomes less likely to occur. As a result, there is a tendency that the number of three-dimensional crosslinks becomes too small and a strength of the thermosetting polyurethane resin to be obtained as a final product becomes lowered.

In one preferable embodiment, the ionomer resin is used as the resin component for the cover composition. Examples of the ionomer resin are one prepared by neutralizing at least a part of carboxyl groups in a copolymer composed of ethylene and α,β-unsaturated carboxylic acid with a metal ion, or one prepared by neutralizing at least a part of carboxyl groups in a terpolymer composed of ethylene, α,β-unsaturated carboxylic acid and α,β-unsaturated carboxylic acid ester with a metal ion. Examples of the α,β-unsaturated carboxylic acid are acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid. Among them, acrylic acid and methacrylic acid are preferable. Examples of the α,β-unsaturated carboxylic acid ester are methyl ester, ethyl ester, propyl ester, n-butyl ester, isobutyl ester and the like of acrylic acid, methacrylic acid, fumaric acid, maleic acid, and the like. Especially, the ester of acrylic acid and methacrylic acid are preferable. Examples of the metal ion for neutralizing at least a part of the carboxyl groups include alkali metal ions such as sodium, potassium, and lithium ions; divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium ions; trivalent metal ions such as aluminum ion, or other metal ions such as tin, and zirconium ions. Among them, sodium, zinc, and magnesium ions are preferably used to improve the resilience and the durability.

Examples of the ionomer resin include, but not limited to, HIMILAN 1555, HIMILAN 1557, HIMILAN 1605, HIMILAN 1652, HIMILAN 1702, HIMILAN 1705, HIMILAN 1706, HIMILAN 1707, HIMILAN 1855, and HIMILAN 1856 available from MITSUI-DUPONT POLYCHEMICAL CO.; SURLYN 8945, SURLYN 9945, and SURLYN 6320 available from DUPONT CO.; and IOTEK 8000, and IOTEK 7010 available from Exxon Co. These ionomer resins exemplified above may be used alone, or as a mixture of two or more.

It is also a preferred embodiment to use another thermoplastic elastomer as a resin component of the cover composition of the present invention in addition to the base resin such as the thermoplastic polyurethane resin or the ionomer resin.

Specific examples of the other thermoplastic elastomers include a thermoplastic polyamide elastomer having a commercial name of “PEBAX (e.g. “PEBAX 2533”)” available from ARKEMA Inc, a thermoplastic polyester elastomer having a commercial name of “HYTREL (e.g. “HYTREL 3548” and “HYTREL 4047”)” available from DU PONT-TORAY Co, a thermoplastic polystyrene elastomer having a commercial name of “Rabalon” available from Mitsubishi Chemical Corporation, and the like. Among them, the thermoplastic polystyrene elastomer is preferred. Examples of the thermoplastic polystyrene elastomer include a polystyrene-diene type block copolymer which contains a polystyrene block component as a hard segment and a diene block component such as polybutadiene, isoprene, hydrogenated polybutadiene, and hydrogenated polyisoprene as a soft segment. The polystyrene-diene type block copolymer is one having a double bond derived from a conjugated diene compound of a block copolymer or a partially hydrogenated block copolymer. Examples of the polystyrene-diene type block copolymer include a block copolymer of SBS (styrene-butadiene-styrene) structure having a polybutadiene block, or a block copolymer of SIS (styrene-isoprene-styrene) structure. An amount of the thermoplastic elastomer to be blended is preferably 1 to 60 parts by mass, more preferably 1 to 35 parts by mass based on 100 parts by mass of the base resin.

When the luster material is blended in the cover, a content of the luster material in the cover composition is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, even more preferably 0.3 part by mass or more and preferably 5 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.0 parts by mass or less based on 100 parts by mass of the resin component. If the content of the luster material is more than 5 parts by mass, a weld line appears clearly after the molding, so that an appearance and durability may be lowered. If the content of the luster material is less than 0.1 part by mass, sufficient luster cannot be obtained.

It is also a preferred embodiment to add a pigment, in addition to the luster material, to the cover, so that a cover having various colors and the luster can be obtained. The pigment may be an organic pigment or an inorganic pigment.

Examples of the pigment include a black pigment such as carbon black; a white pigment such as titanium oxide; a blue pigment such as ultramarine blue, cobalt blue, and phthalocyanine blue; a purple pigment such as anthraquinone violet, dioxane violet, and methyl violet; a yellow pigment such as titanium yellow (20TiO₂—NiO-Sb₂O₃), lead oxide (PbO), chrome yellow (PbCrO₄), yellow iron oxide (FeO(OH)), cadmium yellow, pigment yellow-1, and pigment yellow-12; and a red pigment such as iron oxide red (Fe₂O₃), red lead (Pb₃O₄), molybdenum red, cadmium red, pigment red-3, pigment red-57, pigment orange-13. These pigments may be used alone or as a mixture of two or more kinds.

Specific examples of the pigment include a red pigment such as ZQ-13 commercially available from DAYGLO, a blue pigment such as ZQ-19 commercially available from DAYGLO, an orange pigment such as ZQ-14 commercially available from DAYGLO, a pink pigment such as ZQ-11 commercially available from DAYGLO, and a green pigment such as ZQ-18 commercially available from DAYGLO.

A content of the pigment in the cover composition is preferably 0.001 part by mass or more, more preferably 0.005 part by mass or more, even more preferably 0.01 part by mass or more based on 100 parts by mass of the resin component, and preferably 10 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less. If the content of the pigment is more than 10 parts by mass, the durability of the cover may be lowered. If the content of the pigment is less than 0.001 part by mass, a desired color will not be obtained clearly.

It is also a preferred embodiment of the present invention to use a white pigment together with a colored pigment other than white. In such a case, the content of the colored pigment other than white in the cover composition is preferably 0.001 part by mass or more, more preferably 0.005 part by mass or more and 5 parts by mass or less, more preferably 3 parts by mass or less based on 100 parts by mass of the resin component. If the content of the pigment is more than 5 parts by mass, the durability of the cover may become lowered. On the other hand, if the content of the pigment is less than 0.001 part by mass, a desired color cannot be obtained clearly.

A content of the white pigment (preferably titanium oxide) in the cover composition is 0.005 part by mass or more, more preferably 0.05 part by mass or more, even more preferably 0.1 part by mass or more based on 100 parts by mass of the resin component. If the content of the white pigment (preferably titanium oxide) is 0.005 part by mass or more, a contour of a dimple of the cover becomes clear. The content of the white pigment (preferably titanium oxide) in the cover composition is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less based on 100 parts by mass of the resin component. If the content of the white pigment (preferably titanium oxide) becomes too large, there may be a case in which opacity becomes too high, so that the luster of the luster material in the cover is undermined.

The cover composition of the present invention may further contain a gravity adjusting agent such as calcium carbonate and barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent brightener or the like to the extent that the performance of the cover is not undermined.

A thickness of the cover of the present invention is not particularly limited, and it is preferably 0.3 mm or more, more preferably 0.5 mm or more, even more preferably 0.8 mm or more, and preferably 2.3 mm or less, more preferably 2.0 mm or less, even more preferably 1.6 mm or less. If it is less than 0.3 mm, molding of the cover may become difficult. If it is more than 2.3 mm, the cover becomes too thick and thus the resilience of the resultant golf ball may become lowered.

The core for the golf ball of the present invention is preferably a core (preferably spherical core) molded by heat-pressing the rubber composition for the core containing a base rubber, a crosslinking initiator, a co-crosslinking agent, and, as necessary, a filler.

As the base rubber, a natural rubber and/or a synthetic rubber such as a polybutadiene rubber, a natural rubber, a polyisoprene rubber, a styrene polybutadiene rubber, and ethylene-propylene-diene terpolymer (EPDM) may be used. Among them, typically preferred is the high cis-polybutadiene having cis-1,4 bond in a proportion of 40% or more, more preferably 70% or more, even more preferably 90% or more in view of its superior repulsion property.

The crosslinking initiator is blended to crosslink the base rubber component. As the crosslinking initiator, an organic peroxide is preferably used. Examples of the organic peroxide for use in the present invention are dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Among them, dicumyl peroxide is preferable. The amount of the organic peroxide to be blended in the rubber composition is preferably 0.2 part by mass or more, more preferably 0.3 part by mass or more, and preferably 3 parts by mass or less, more preferably 2 parts by mass or less based on 100 parts by mass of the base rubber. If the content is less than 0.2 part by mass, the core becomes too soft, and the resilience tends to be lowered, and if the content is more than 3 parts by mass, the amount of co-crosslinking agent needs to be increased in order to obtain an appropriate hardness, so that the resilience tends to be insufficient.

The co-crosslinking agent is not particularly limited as long as it has the effect of crosslinking a rubber molecule with a base rubber molecular chain by graft polymerization; for example, α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof, more preferably, acrylic acid, methacrylic acid or a metal salt thereof may be used. As the metal constituting the metal salt, for example, zinc, magnesium, calcium, aluminum and sodium may be used, and among them, zinc is preferred because it provides high resilience. The amount of the co-crosslinking agent to be used is preferably 10 parts or more, more preferably 20 parts or more, and preferably 50 parts or less, more preferably 40 parts or less based on 100 parts of the base rubber by mass. If the amount of the co-crosslinking agent to be used is less than 10 parts by mass, the amount of the organic peroxide must be increased to obtain an appropriate hardness which tends to lower the resilience. On the other hand, if the amount of the co-crosslinking agent to be used is more than 50 parts by mass, the core becomes too hard, so that the shot feeling may be lowered.

The filler contained in the rubber composition for the core is mainly blended as a gravity adjusting agent in order to adjust the specific gravity of the golf ball obtained as the final product in the range of 1.0 to 1.5, and may be blended as required. Examples of the filler include an inorganic filler such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. The amount of the filler to be blended in the rubber composition is preferably 2 parts or more, more preferably 3 parts or more, and preferably 50 parts or less, more preferably 35 parts or less based on 100 parts of the base rubber by mass. If the amount of filler to be blended is less than 2 parts by mass, it becomes difficult to adjust the weight, while if it is more than 50 parts by mass, the weight ratio of the rubber component becomes small and the resilience tends to be lowered.

The rubber composition for the core may further include an organic sulfur compound, an antioxidant, or a peptizing agent as required in addition to the base rubber, the crosslinking initiator, the co-crosslinking agent, and the filler.

As the organic sulfur compound, a diphenyl disulfide or a derivative thereof may be preferably used. The amount of the diphenyl disulfide or the derivative thereof to be blended is preferably 0.1 part or more, more preferably 0.3 part or more, and preferably 5.0 parts or less, more preferably 3.0 parts or less based on 100 parts of the base rubber by mass. Examples of the diphenyl disulfide or the derivative thereof include diphenyl disulfide, a mono-substituted diphenyl disulfide such as bis(4-chlorophenyl) disulfide, bis(3-chlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(3-bromophenyl) disulfide, bis(4-fluorophenyl) disulfide, bis(4-iodophenyl) disulfide and bis(4-cyanophenyl) disulfide; a di-substituted diphenyl disulfide such as bis(2,5-dichlorophenyl) disulfide, bis(3,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, bis (3,5-dibromophenyl) disulfide, bis(2-chloro-5-bromophenyl) disulfide, and bis(2-cyano-5-bromophenyl) disulfide; tri-substituted diphenyl disulfide such as bis (2,4,6-trichlorophenyl) disulfide, and bis (2-cyano-4-chloro-6-bromophenyl) disulfide; a tetra-substituted diphenyl disulfide such as bis (2,3,5,6-tetra chlorophenyl) disulfide; a penta-substituted diphenyl disulfide such as bis(2,3,4,5,6-pentachlorophenyl) disulfide and bis(2,3,4,5,6-penta bromophenyl) disulfide. These diphenyl disulfide or the derivatives thereof can enhance resilience by having some influence on the state of vulcanization of vulcanized rubber. Among them, diphenyl disulfide and bis(penta bromophenyl) disulfide are preferably used since the golf ball having particularly high resilience can be obtained.

An amount of the antioxidant to be blended is preferably 0.1 part by mass or more and 1 part by mass or less based on 100 parts by mass of the base rubber. An amount of the peptizing agent is preferably 0.1 part by mass or more and 5 parts by mass or less based on 100 parts by mass of the base rubber.

The conditions for press-molding the rubber composition should be determined depending on the rubber composition. The press-molding is preferably carried out for 10 to 60 minutes at the temperature of 130 to 200° C. Alternatively, the press-molding is preferably carried out in a two-step heating, for example, for 20 to 40 minutes at the temperature of 130 to 150° C., and continuously for 5 to 15 minutes at the temperature of 160 to 180° C.

If the golf ball of the present invention is a three-piece golf ball or a multi-piece golf ball, the core consists of a center made from the above-mentioned rubber composition for the core and at least one intermediate layer covering the center. Examples of the intermediate layer include a thermoplastic resin such as a polyurethane resin, an ionomer resin, nylon, and polyethylene; and a thermoplastic elastomer such as a polystyrene-based elastomer, a polyolefin-based elastomer, a polyurethane-based elastomer, a polyester-based elastomer and the like. Among them, the ionomer resin is preferable.

The intermediate layer may further contain a gravity adjusting agent such as tungsten, and barium sulfate, an antioxidant, a pigment and the like, in addition to the resin component.

When preparing a wound-core golf ball in the present invention, a wound core may be used as the core. In that case, for example, a wound core comprising a center formed by curing the above rubber composition for the core and a rubber thread layer which is formed by winding a rubber thread around the center in an elongated state can be used. In the present invention, the rubber thread, which is conventionally used for winding around the center, can be adopted for winding around the center. The rubber thread, for example, is obtained by vulcanizing a rubber composition including a natural rubber, or a mixture of a natural rubber and a synthetic polyisoprene, a sulfur, a vulcanization auxiliary agent, a vulcanization accelerator, and an antioxidant. The rubber thread is wound around the center in elongation of about 10 times length to form the wound core.

EXAMPLES

The following examples illustrate the present invention; however, these examples are intended to illustrate the invention and are not to be construed to limit the scope of the present invention. Many variations and modifications of such examples will exist without departing from the scope of the inventions. Such variations and modifications are intended to be within the scope of the invention.

[Evaluation] (1) Evaluation of Weld Line

Thirty golfers visually examined the golf ball bodies formed with the paint films to evaluate the appearance of the weld line based on the following evaluation standards.

None: Weld lines are inconspicuous and appearance was good. Present: Weld lines are clearly discernible, and appearance is unfavorable.

(2) Luster

Thirty golfers visually examined the golf balls formed with a paint film to evaluate the luster based on following evaluation standards.

E(Excellent): There is a marked pearl luster quality, and appearance is very beautiful. G(Good): There is a pearl luster quality, and appearance is beautiful. F(Fair): There is a poor pearl luster quality, and appearance is not very good. P(Poor): There is essentially no pearl luster quality, and appearance is poor.

(3) Coating Workability and Unevenness of Paint Application

A spray gun (SA-100 manufactured by Fuji Toryo) was connected to a paint line having a strainer provided with a metal mesh of 120 μm in a middle thereof to evaluate workability when applying the paint and unevenness of the formed paint film based on following evaluation standards.

Coating Workability

G(Good): There is no clogging of the strainer and the spray gun on the paint line. P(Poor): Clogging of the strainer and the spray gun on the paint line is occasionally found, resulting in unstable state of application.

Unevenness of the Paint Film

G(Good): There is no unevenness of the paint film, and appearance of the golf ball is good. P(Poor): Unevenness of the paint film was found at some portions, resulting in poor appearance of the golf ball.

(4) Durability of the Golf Ball

Each golf ball was repeatedly hit with a metal head driver (W#1) attached to a swing robot manufactured by TRUETEMPER CO, at the head speed of 45 m/sec. to make the golf ball collide with a collision board. Times up to which the golf balls are cracked were measured. In addition, each value obtained was reduced to an index number relative to the measured value obtained in Golf ball No. 11 being assumed 100. The larger number indicates better durability.

(5) Durability of the Paint Film of Golf Ball

Each golf ball was repeatedly hit 50 times with a metal head driver (#W1) attached to a swing robot manufactured by TRUETEMPER CO, at the head speed of 45 m/sec. to evaluate appearance of the golf ball after being hit based on following evaluation standards.

G(Good): No crack is present on a surface of the golf ball. F(Fair): Cracks are found at some portions of the surface of the golf ball, but the paint film is not peeled off. P(Poor): Cracks are found on the surface of the golf ball, and the paint film is peeled off.

[Preparation of Golf Ball Body] (1) Preparation of Core

The rubber composition shown in Table 1 was kneaded and pressed with upper and lower molds each having a spherical cavity at the heating condition of 160° C. for 20 minutes to obtain the core in a spherical shape having a diameter of 38.5 mm.

TABLE 1 Rubber composition for the core Part by mass Polybutadiene rubber 100 Zinc oxide 20 Zinc acrylate 22.0 Barium sulfate Appropriate amount*⁾ Dicumyl peroxide 1 Formulation: parts by mass Barium sulfate: prepared such that a mass of the golf ball becomes 45.5 g Notes on Table 1 Polybutadiene rubber: BR730 manufactured by JSR Corporation Zinc acrylate: ZNDA-90S manufactured by NIHON JYORYU KOGYO Co., LTD. Zinc oxide: “Ginrei R” manufactured by Toho-Zinc Co. Barium sulfate: Barium sulfate BD manufactured by Sakai Chemical Industry Co., Ltd. Dicumyl peroxide: Percumyl D manufactured by NOF Corporation

(2) Preparation of Cover Composition

The materials shown in Table 2 were mixed using a twin-screw kneading extruder to obtain the cover composition in the form of pellet. The extrusion was conducted in the following conditions: screw diameter=45 mm, screw revolutions=200 rpm, screw L/D=35, and the cover composition was heated to from 160° C. to 230° C. at the die position of the extruder.

(3) Preparation of the Golf Ball Body

The cover composition thus prepared was directly injection-molded onto the core to form the cover covering the core, thereby obtaining the two-piece golf ball having a diameter of 42. 7 mm. The upper and lower molds for forming the cover have a spherical cavity with dimples. The part of the dimples can serve as a hold pin which is retractable. When forming the golf ball body, the hold pins were protruded to hold the core, and the resin heated at 210° C. was charged into the mold held under the pressure of 80 tons for 0.3 seconds. After the cooling for 30 seconds, the molds were opened and then the golf ball was discharged.

TABLE 2 Golf ball No. 1 2 3 4 5 6 7 8 9 10 Cover layer Himilan 1605 50 50 50 50 50 50 50 50 50 50 Himilan 1706 50 50 50 50 50 50 50 50 50 50 Pigment: white pigment (titanium dioxide) — — — — — — 2 — — — Pigment: blue pigment ZQ-19 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Iriodin 201 (particle size of 5 to 25 μm) 0.5 0.1 0.5 0.5 0.5 0.05 0.5 — — — Iriodin 215 (particle size of 10 to 60 μm) — — — — — — — 0.5 — — Iriodin 351 (particle size of 5 to 100 μm) — — — — — — — — 0.5 — Iriodin 355 (particle size of 10 to 100 μm) — — — — — — — — — 0.5 Iriodin 163 (particle size of 20 to 180 μm) — — — — — — — — — — Iriodin 249 (particle size of 10 to 125 μm) — — — — — — — — — — Iriodin 183 (particle size of 45 to 500 μm) — — — — — — — — — — Paint film layer Two-component curing type polyurethane 100 100 100 100 100 100 100 100 100 100 resin Iriodin 201 (particle size of 5 to 25 μm) 10 10 1 20 22 10 1 10 10 10 Iriodin 215 (particle size of 10 to 60 μm) — — — — — — — — — — Iriodin 351 (particle size of 5 to 100 μm) — — — — — — — — — — Iriodin 355 (particle size of 10 to 100 μm) — — — — — — — — — — Iriodin 163 (particle size of 20 to 180 μm) — — — — — — — — — — Iriodin 249 (particle size of 10 to 125 μm) — — — — — — — — — — Iriodin 183 (particle size of 45 to 500 μm) — — — — — — — — — — Evaluation Luster E E G E E G G E E E Weld line None None None None None None None None None None Coating workability G G G G G G G G G G Unevenness of paint film G G G G P G G G G G Durability of paint film G G G G F G G G G G Durability of golf ball 100 101 100 100 100 102 100 101 101 100 Golf ball No. 11 12 13 14 15 16 17 18 Cover layer Himilan 1605 50 50 50 50 50 50 50 50 Himilan 1706 50 50 50 50 50 50 50 50 Pigment: white pigment (titanium dioxide) — — 0.2 — — — — — Pigment: blue pigment ZQ-19 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Iriodin 201 (particle size of 5 to 25 μm) 0.5 — 0.5 0.5 — — — 0.5 Iriodin 215 (particle size of 10 to 60 μm) — — — — — — — — Iriodin 351 (particle size of 5 to 100 μm) — — — — — — — — Iriodin 355 (particle size of 10 to 100 μm) — — — — — — — — Iriodin 163 (particle size of 20 to 180 μm) — — — — — 0.5 — — Iriodin 249 (particle size of 10 to 125 μm) — — — — — — 0.5 — Iriodin 183 (particle size of 45 to 500 μm) — 0.5 — — — — — — Paint film layer Two-component curing type polyurethane 100 100 100 100 100 100 100 100 resin Iriodin 201 (particle size of 5 to 25 μm) — 10 10 — 10 10 10 — Iriodin 215 (particle size of 10 to 60 μm) — — — — — — — — Iriodin 351 (particle size of 5 to 100 μm) — — — — — — — — Iriodin 355 (particle size of 10 to 100 μm) — — — — — — — — Iriodin 163 (particle size of 20 to 180 μm) — — — — — — — — Iriodin 249 (particle size of 10 to 125 μm) — — — — — — — 10 Iriodin 183 (particle size of 45 to 500 μm) 10 — — — — — — — Evaluation Luster E G E F F G G G Weld line None Present None Present None Present Present None Coating workability P G G G G G G G Unevenness of paint film P G G G G G G P Durability of paint film P G G G G G G F Durability of golf ball 100 97 100 100 100 98 100 100 Formulation: parts by mass

Notes on Table 2

Himilan 1605: a sodium ion-neutralized ethylene-methacrylic acid copolymer-based ionomer resin manufactured by MITSUI-DUPONT POLYCHEMICAL Himilan 1706: a zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by MITSUI-DUPONT POLYCHEMICAL Iriodin 201: a pearl pigment manufactured by MERCK (a luster material comprising mica as a core layer and titanium oxide covering a surrounding area of the core layer; a particle size of 5 μm to 25 μm) Iriodin 215: a pearl pigment manufactured by MERCK (a luster material comprising mica as a core layer and titanium oxide covering a surrounding area of the core layer; a particle size of 10 μm to 60 μm) Iriodin 351: a pearl pigment manufactured by MERCK (a luster material comprising mica as a core layer and titanium oxide covering a surrounding area of the core layer; a particle size of 5 μm to 100 μm) Iriodin 355: a pearl pigment manufactured by MERCK (a luster material comprising mica as a core layer and titanium oxide covering a surrounding area of the core layer; a particle size of 10 μm to 100 μm) Iriodin 163: a pearl pigment manufactured by MERCK (a luster material comprising mica as a core layer and titanium oxide covering a surrounding area of the core layer; a particle size of 20 μm to 180 μm) Iriodin 249: a pearl pigment manufactured by MERCK (a luster material comprising mica as a core layer and titanium oxide covering a surrounding area of the core layer; a particle size of 10 μm to 125 μm) Iriodin 183: a pearl pigment manufactured by MERCK (a luster material comprising mica as a core layer and titanium oxide covering a surrounding area of the core layer; a particle size of 45 μm to 500 μm) Titanium dioxide: a titanium oxide A-220 manufactured by ISHIHARA SANGYO KAISHA, LTD. ZQ-19: a blue pigment manufactured by DAYGLO

[Formation of the Paint Film]

A mark was pad-printed on a surface of the golf ball body and subsequently, the composition for forming paint film shown in Table 2 was applied thereto to cover the golf ball body, followed by drying in an oven at 40° C. for 4 hours, thereby preparing a golf ball. The composition for forming a paint film was prepared in a following manner.

[Preparation of the Composition for Forming the Paint Film]

1) Base resin: urethane polyol

Into 120 parts by mass of a solvent (toluene and methylethyl ketone), 60 parts by mass of PTMG250 (polyoxytetramethylene glycol having a molecular weight of 250 manufactured by BASF) and 54 parts by mass of 550 U (branched polyol having a molecular weight of 550 manufactured by Sumika Bayer Urethane Co., Ltd.) were dissolved, and then dibutyl tin dilaurylate was added to the mixture in a ratio of 0.1 mass % relative to a total base resin. While the polyol was maintained at 80° C., 66 parts by mass of isophorone diisocyanate was dropped thereto, thereby preparing a urethane polyol (having a solid content of 60 mass %, a hydroxyl group value of 75 mgKOH/g, and a weight average molecular weight of 7808).

2) Curing agent: isophorone diisocyanate (manufactured by Sumika Bayer Urethane Co., Ltd.) 3) Blending ratio: NCO of curing agent/OH of base resin=1.2 (molar ratio) 4) A luster material was added to 100 parts by mass of the two-component curing type urethane resin component as shown in Table 2, thereby preparing a composition for forming a paint film.

Table 2 shows the results of evaluation of luster, presence of weld line, coating workability, unevenness of paint film, and durability of the resultant golf balls.

Golf ball Nos. 1 to 4, Nos. 6 to No. 10, and No. 13 are golf balls having a golf ball body and a paint film covering the golf ball body, wherein the golf ball body and the paint film contains a luster material having a particle size of 5 μm to 100 μm. In any case, a golf ball having luster and good appearance and durability without a conspicuous weld line was obtained. Coating workability was also good and there was no unevenness of the paint film.

Golf ball No. 5 is a case in which the paint film contains more than 20 parts by mass of the luster material based on 100 parts by mass of the resin component constituting the paint film, in which there was a tendency that unevenness of the paint film was formed. Golf ball No. 6 is a case in which the cover contains less than 0.1 part by mass of the luster material based on 100 parts by mass of the resin component constituting the cover, in which there was a tendency that the luster was lowered compared with Golf ball No. 2.

Golf balls No. 11 and No. 18 are cases in which the paint film contains a luster material having a particle size of 45 μm to 500 μm and 10 μm to 125 μm respectively, where unevenness of the paint film occurred. Golf ball No. 12 is a case in which the cover contains a luster material having a particle size of 45 μm to 500 μm, where weld lines were conspicuous and appearance was poor. Golf ball No. 14 is a case where only the cover contained the luster material, while Golf ball No. 15 is a case where only the paint film contained the luster material. In both cases, the luster was insufficient. Golf ball Nos. 16 and No. 17 are cases in which the cover contained a luster material having a particle size which is outside the range of 5 μm to 100 μm, where weld lines were conspicuous and appearance was poor.

The present invention provides a golf ball having luster and durability.

This application is based on Japanese Patent application No. 2, 007-18,444 filed on Jan. 29, 2007, the contents of which are hereby incorporated by reference. 

1. A golf ball having a golf ball body and a paint film covering the golf ball body, wherein each of the golf ball body and the paint film contains a luster material having a particle size of 5 μm to 100 μm.
 2. The golf ball according to claim 1, wherein the luster material comprises mica as a core layer and a light-reflective material covering a surrounding area of the core layer.
 3. The golf ball according to claim 1, wherein the luster material comprises mica as the core layer and a light-reflective material consisting of titanium oxide or iron oxide covering a surrounding area of the core layer.
 4. The golf ball according to claim 1, wherein the golf ball body comprises a cover and the cover contains 0.1 part to 5 parts by mass of the luster material with respect to 100 parts by mass of the resin component constituting the cover.
 5. The golf ball according to claim 1, wherein the paint film contains 1 part to 20 parts by mass of the luster material based on 100 parts by mass of the resin component contained in the paint film.
 6. The golf ball according to claim 1, wherein the luster material has a particle size of 5 μm to 60 μm.
 7. The golf ball according to claim 1, wherein the paint film is a two-component curing type polyurethane resin.
 8. The golf ball according to claim 1, wherein the golf ball body has a cover and the cover contains the luster material, a white pigment, and a colored pigment other than white.
 9. The golf ball according to claim 8, wherein the colored pigment is a blue pigment or a red pigment.
 10. The golf ball according to claim 1, wherein the cover has a thickness of 0.3 mm to 2.3 mm.
 11. A golf ball having a golf ball body consisting of a core and a cover covering the core and a paint film covering the golf ball body, wherein each of the cover and the paint film contains a luster material having a particle size of 5 μm to 100 μm.
 12. The golf ball according to claim 11, wherein the luster material comprises mica as a core layer and a light-reflective material consisting of titanium oxide or iron oxide covering a surrounding area of the core layer.
 13. The golf ball according to claim 12, wherein the cover contains 0.1 part to 5 parts by mass of the luster material with respect to 100 parts by mass of the resin component constituting the cover.
 14. The golf ball according to claim 13, wherein the paint film contains 1 part to 20 parts by mass of the luster material based on 100 parts by mass of the resin component contained in the paint film.
 15. The golf ball according to claim 14, wherein the paint film is a two-component curing type polyurethane resin.
 16. The golf ball according to claim 14, wherein the luster material has a particle size of 5 μm to 60 μm.
 17. The golf ball according to claim 14, wherein the golf ball body has a cover and the cover contains the luster material, a white pigment, and a colored pigment other than white.
 18. The golf ball according to claim 17, wherein the colored pigment is a blue pigment or a red pigment.
 19. The golf ball according to claim 14, wherein the cover has a thickness of 0.3 mm to 2.3 mm. 